1. Field of the Invention
The invention relates to a drum housing for a working drum of a construction machine or mining machine, said working drum being provided with tools and rotating about a drum axis with a specified direction of rotation, a construction machine or mining machine with such drum housing, as well as a method for monitoring the condition of a working drum of a construction machine/mining machine or of the tools thereof arranged on the circumference of the working drum by measuring the condition of the working drum or of the tools thereof by means of a monitoring device.
2. Description of the Prior Art
Such method is known from DE 10 2008 045 470 A1 (U.S. Pat. No. 8,386,196). A monitoring device monitors the condition of the tools of a road milling machine through at least one inspection opening in a housing shell of a drum housing, with said housing shell at least partially enclosing the circumference of the working drum.
The working drum of a construction machine being provided with tools and rotating about a drum axis, for example, a milling drum during the working of road surfaces by means of road milling machines, as well as for the mining of deposits by means of surface miners, is subject to a continuous process of wear and tear, where a tool breakage may also occur. This concerns mainly the tools used, and in particular the milling tools, but also the toolholders. When the tools reach a certain state of wear, it is advisable to replace the tools as the ongoing process will otherwise lose in efficiency. In this regard, a distinction needs to be made between different states of wear which lead to the replacement of a milling tool or milling toolholder respectively:    1. Replacement of the milling tool as there is no longer sufficient wear material, especially carbide metal in the tip. The penetration resistance becomes too great, which leads to the efficiency decreasing as a result of excessive friction loss. Wear and tear is mainly rotationally symmetrical.    2. Replacement of the toolholder as between the milling tool and holder, at the contact surface between these parts, wear and tear in particular of the holder occurs and the wear limit has been reached. This type of wear and tear is usually symmetrical.    3. Non-rotationally symmetrical wear and tear of the milling tool tip and/or the milling tool head caused by insufficient rotational movement of the milling tool during the milling process. This results in a poor milling pattern and the risk of a tool breakage as the supporting effect of the milling tool head is lost.    4. Furthermore, the toolholder may be subject to additional, non-rotationally symmetrical wear and tear.    5. Tool breakage.
Furthermore, worn-out and/or broken milling tools can result in secondary damage to the toolholders, or worn-out toolholders, respectively, can result in secondary damage to the milling drum. Timely replacement of the milling tools and/or toolholders may therefore be necessary and can reduce costs. Replacing the milling tools and/or toolholders too early, on the other hand, also means not working at optimal cost. In such a case, existing wear potential is not utilized appropriately. Previously, without any monitoring device, the state of wear of the milling drum and the tools, namely, the milling tools and toolholders, was assessed by means of a visual check performed by the machine operator. To do so, the machine operator needs to park the machine (turn off engine and uncouple drum from the drive train). He then needs to open the rear drum plate in order to visually inspect the milling drum.
The milling drum is then turned by means of a second drive (auxiliary drive) in order to be able to inspect, section by section, the entire milling drum. The task of inspecting the drum may also be undertaken by a second operator. In the process, the state of wear of the toolholders is usually assessed via so-called wear markings, while the state of wear of the milling tools is assessed via the wear in tool length and the rotational symmetry of the wear pattern.
Checking the state of wear of the milling tool and holder is very time-consuming and reduces the operating time of the machine. In addition, there is the risk, owing to the fact that the assessment is highly subjective in nature, of the state of wear of the holder and milling tool not being assessed correctly and the wear potential therefore not being optimally utilized.
According to the known prior art apparent from FIG. 2, a lens barrel of the inspection camera of the monitoring device is guided into the interior of the drum housing through the housing shell of the drum housing. In addition, it is intended for the monitoring device to be stowed in a protection device during the milling process. The lens barrel inside the drum housing is subject to a high degree of wear and tear caused by the revolving milled material and may be heavily damaged by larger fragments of the milled material. Damage caused to the optics of the camera through the lens barrel can also not be excluded if the camera is not removed during the milling operation. Replacing damaged parts is time-consuming. In addition, mounting times are incurred by the stowing, or mounting respectively, of the monitoring device.
To solve this problem, DE 10 2011 016 271 A proposes to provide inspection openings for a monitoring device in a housing shell of the drum housing, with a closing mechanism being arranged on the outer side of the housing shell that enables closure of the at least one inspection opening.
It has turned out that the milled material revolving in the drum housing during the milling operation builds up a very high pressure which causes the milled material to be hurled against the inner side of the housing shell at high speed so that the closing mechanism can easily be damaged.